The present invention relates to a nozzle cleaning device for an ink jet printer having a plurality of ink reservoirs, the cleaning device including a pressure source and a valve mechanism for selectively coupling the pressure source to the ink reservoirs.
An ink jet printer typically contains a plurality of printheads, e.g. at least one for each color in the case of a multi-color printer. Each printhead has an array of nozzles through which ink droplets can be jetted out onto a recording medium, and also ink reservoirs that are in communication with each of the nozzles of the nozzle array through respective ink channels. In or adjacent to each of the ink channels an actuator, e.g. a piezoelectric actuator is provided which may be energized in order to generate a pressure wave in the liquid ink in the ink channel, so that an ink droplet is expelled from the associated nozzle.
In some known ink jet printing systems, the ink reservoir is maintained under a slight subatmospheric pressure in order to prevent ink from leaking out of the nozzles.
Since the minute nozzles tend to become clogged with impurities, it is necessary to clean the nozzles from time to time. This is normally achieved by moving the printhead to a cleaning station and then applying a positive pressure to the ink reservoir in order to flush the nozzles with ink from the ink reservoir. The cleaning station includes a gutter which faces the nozzles of the printhead for collecting the ink that is ejected out of the nozzles in the flushing step, and may also include a wiper for removing remnants of ink and dust from the nozzle face of the printhead. Another purpose of such a cleaning or flushing procedure is to remove air bubbles that may have entered into the ink channels and which can have an adverse effect on the jetting properties of the nozzles.
In order to limit the required capacity of the pressure source and the dimensions of the cleaning station, it is preferable that the printheads are not cleaned simultaneously but are cleaned individually by applying pressure only to one ink reservoir at a time when the nozzles connected to this particular ink reservoir are in a position facing the ink collecting system of the cleaning station. This also has the advantage that the amount of waste ink can be reduced by performing the cleaning process only for the printhead or printheads that actually need a cleaning treatment. In this situation, however, a valve mechanism is required for connecting the pressure source selectively to the ink reservoir of the printhead that is being cleaned. Such a valve mechanism adds to the complexity and costs of the system as a whole, in particular since valves of the direct-driven type ought to be employed in view of the generally small differential pressures involved.
U.S. Pat. No. 6,095,633 discloses a cleaning device of the type described above, in which a separate valve is provided for each of the ink reservoirs in order to controllably connect the valves to a common pressure source.
U.S. Pat. No. 4,870,431 discloses a cleaning device for a hot-melt ink jet printer having a rotating printhead with nozzles arranged at the outer periphery thereof for printing onto a sheet of recording paper that has been wrapped around the printhead. Here, the interior of the printhead is subdivided into a plurality of ink reservoirs each having the cross-sectional shape of a sector of a circle. Each reservoir has a supply opening in its top face, so that solid pellets of ink may be dropped into the ink reservoir where the ink is molten. By rotating the printhead, each reservoir opening may be brought into a position where it is aligned with and sealingly connected to an air supply system. When the printhead is locked in this position, pressurized air is supplied into the ink reservoir for flushing the nozzles connected thereto. The rest of the top face of the printhead is covered by a stationary lid for closing off the openings of the ink reservoirs that are not in the cleaning position.